Activity in Number of Shares of Common Stock Issued and Outstanding (Detail)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Reconciliation of Common Stock Outstanding [Line Items]
At beginning of year	193,723,208		192,836,008		191,115,378
Stock options exercised	482,974	[1]	615,674	[1]	1,495,926	[1]
Employee stock purchase and thrift plans	78,389		33,390		49,657
Restricted stock awards, net of forfeitures	224,296		238,136		175,047
Treasury shares purchased	(3,867,550)		0		0
At end of year	190,641,317		193,723,208		192,836,008

[1] Shares issued upon exercise of stock options are less than the amount reflected in Note I due to withholdings for statutory income taxes owed upon exercise.